(a) Field of the invention
The present invention relates to air distillation columns of the type utilizing on at least part of their height, stacks of packs of organized lining of the cross-undulating type, each pack comprising a bundle of rectangular undulating lamellar sheets each being placed in a generally vertical plane and against one another, the waves of each lamellar sheet being oblique and downwardly directed, in opposite directions from one lamellar sheet to the next one, from a high vertical edge to a low vertical edge of the lamellar sheet.
(b) Description of prior art
Recent developments in the technique of air distillation have consisted in utilizing linings, for example organized linings of the so-called "cross-undulating" type, instead of traditional distillation plates. These linings have indeed an important advantage from the point of view of loss of charge, and consequently permit substantial savings in the operation of the plant. On the other hand, these linings give rise to various technological problems, which are associated in particular with the so-called "partition effect" phenomenon: the descending liquid tends to accumulate on the periphery of the lining or on the partition surrounding it, and from there to stream down without exchanging heat nor material with the ascending gas. This is detrimental to the uniformity of the composition of the liquid on the section of column, and downgrades the performances of the arrangement.
To reduce these undesired effects, it has been proposed to provide intermediate means for the redistribution of the liquid in each distillation section, defined between a lower fluid inlet/outlet unit and an upper fluid inlet/outlet unit. This increases the complexity of the columns and considerably increases the height thereof, for two reasons: the increase of the number of distributors and the substantial height of each distributor. Such a height increase is particularly costly in the case of cryogenic columns provided with a high performance thermic insulation and may require the use of additional liquid ascending pumps, for example from the mean pressure column to the low pressure column.
The invention aims at enabling air distillation columns utilizing cross-undulating linings to achieve high performances with a substantially reduced height.